The mechanisms used by selected strains of fungi and bacteria to oxidize benzo(a)pyrene, benzo(a)anthracene and methylcholanthrene are being investigated. Metabolites produced by intact organisms will be isolated and chemically characterized. In addition, the metabolism of the above compounds by microsomal preparations from Cunninghamella elegans is under investigation. Attempts will be made to purify the fungal cytochrome P450 enzyme system and the results will be compared to those reported for the liver microsomal enzymes of higher animals.